I receive such a error information: Invalid constraint: {concave} == {real affine} for the code below

```
cvx_begin sdp
variable W(Nt,Nt,K) hermitian;
variable nor(1,K);
minimize(....);
subject to
for k=1:K
[W(:,:,k),W(:,:,k)*h(:,k);
h(:,k)'*W(:,:,k),W(:,:,k)-inv_pos(nor(k))] == hermitian_semidefinite(Nt+1);
[W(:,:,k), W(:,:,k)h(:,k);
h(:,k)'W(:,:,k),inv_pos(1-nor(k))] == hermitian_semidefinite(Nt+1);
W(:,:,k) == hermitian_semidefinite(Nt);
nor(k)>=0;
nor(k)<=1;
end
cvx_end
```

It seems that the use of inv_pos introduces convex expression and consequently causes the mistake. Do anyone knows how to solve the problem or rewrite this constrait?